You aren't correct in saying there's no good music. There IS. The problem is that it is not as easily accessible as it used to be via radio and videos.
As for why that is the case, there are so many reasons.
First and foremost, the music industry is driven by love of MONEY, not music. "Back in the old days," people got signed based on "scenes" (e.g., anyone from England with a guitar got a record deal after Beatlemania hit; anyone standing on the corner of Haight and Ashbury in San Francisco in 1966 got a deal, anyone calling himself/herself a "singer/songwriter" in L.A. got a deal in the late 60s/early 70s, everyone hanging around CBGBs in 1977 got a deal, etc.). The artists who came out of these "scenes" were not all good, but they did have uniqueness to them (e.g., the Grateful Dead, Steve Miller, Boz Scaggs, and the Jefferson Airplane came out of San Francisco; Talking Heads, the Ramones, and Blondie were all CBGBs regulars). Today, that is NOT the case. As Roy Clark opined about modern country music, "Anymore, if you hear a song you like, tomorrow there'll be 20 songs on the radio that sound just like it."
Because of this, the great music that does exist cannot get a commercial (or "mainstream") outlet, which is problem number two. Radio stations, around 1980-82, began what they called a "superstars format." FM rock radio in the 70s was the land of experimentation. A dirty little secret here: the two most overplayed songs in FM rock history (Stairway to Freebird), were NEVER EVER released as "singles." They were long and DJs put them on (along with other long songs like "Funeral for a Friend/Love Lies Bleeding" by Elton John and "Loan Me a Dime" by Boz Scaggs) so they could go to the john and raid the station refrigerator. Then along came the Arbitron books and the aforementioned love of money. And their belief is that "everybody" wants to hear the EXACT SAME four Eagles songs ("Hotel California," "Life in the Fast Lane," "Desperado," and "Take It Easy"), "everyone" wants to hear the EXACT SAME four Fleetwood Mac songs ("The Chain," "Dreams," "Rhiannon," and "Go Your Own Way"), "everyone" wants to hear the EXACT SAME four Bob Seger songs ("Rock and Roll Never Forgets," "Turn the Page," "Night Moves," and "Fire Lake"), etc. -- AND that "everyone" wants to hear the EXACT SAME THIRTY ARTISTS (Eagles, Fleetwood Mac, Seger, Journey, Styx, Zep, Beatles, Stones, AC/DC, Jefferson Airplane, Janis, Doors, Genesis, etc.), so you'll keep listening if they keep playing the same songs and the same artists nonstop. I guess they never stopped to think that the reason all these people became so popular was that PEOPLE GOT THE CHANCE TO HEAR THEM. No such luck anymore.
And that is caused by problem #3: nearly every radio station in this country now is owned by one of two corporations. As such, they are all programmed alike by the same person or group of "consultants" (there's no such thing as "regionalism" anymore), many are nationally broadcast so there's no local DJs anymore (I heard a DJ on the radio in Nashville the other night say, "You know, I'm the only DJ who's on the air live in Nashville right now!"); and, as a result, they play the same songs over and over and over and over, ad naseum. There is no acknowledgement of regionalism, even though it exists (e.g., the BoDeans are extremely popular in their hometown of Milwaukee and their "second home" of Chicago) -- but robots programming and controlling the radio's playlist doesn't allow for that to be reflected on radio!
The bottom line is that the people running the industry want to play it safe and make as much money as humanly possible, so they will create clones of whatever is popular right now (many people refer to it as "cookie-cutter music" because it all sounds the same and the people all dress the same [see: 80s hairbands]) and not allow for fresh music to hit the mainstream airwaves. Sadly, in radio it is called "the LCD factor" -- lowest common denominator. I LOATHE that term because it makes it appear that radio programmers think the listener is stupid, but that's exactly the way they treat the listener -- as though he/she IS stupid.